Liquid paint vs. powdercoat 4

[TJK1]

What can provide a better, more scratch resistant and chip resistant painted surface on an chassis that will be handled and moved from bench to bench many times a day, in doors? Would a MIL-Spec liquid paint or a powder coating be better? If a Mil-Spec liquid paint would be better, which Mil-Spec would you recommend and with which primer spec?
We have some stainless steel PEM studs pressed into the chassis from the outside and were thinking of using Bondo to fill the small gaps on the outside around the PEM studs, and then were planning on using liquid air dried paint. I was told that it is not good to use Bondo if you plan to powdercoat because when you bake the powdercoating it causes the Bondo to deteriorate or crack, which looks bad.
Overall we are mostly concerned with providing the hardest
painted surface we can get on our aluminum chassis. What would you recommend we paint it with?

 

[evelrod]

I've used both methods on the subframes and chassis of the race cars I have built. Your correct in that plastic filler material won't do for powder coating...It'll just get sand blasted out prior to coating anyway.
You can, however, use it if you plan on using paint, just about any painting system. I prefer an etching primer and a top quality polyurethane single coat process. Too much paint will result in a possible chipping problem, at least in the subframes of automobiles. Not a huge problem for me, but some minor chipping does occur.

The last two Mini Cooper subframes I had powder coated in 2003 have held up quite well considering they have been man-handled severely over the last five seasons...a good if costly option as it turns out. Chipping has been minor and no major repairs have been needed.

In favor of polyurethane paint is that it is fairly cheap, can be done "in house" and is easily repairable. I did five Model A Ford wire wheels in 1989 and they still look as if they had been "powder coated".

Powdercoating is more costly, time consuming in so far as it must be done by a professional shop. It is in my experience a very nice finish that is durable if treated like any other painted surface.

Flip a coin.

Rod

 

[MadMango]

A consideration for the PEM studs, they will have to be masked prior to painting. Powder coating will require the use of special plugs & caps (silicone) and high temp tapes. Traditional painting will allow for standard masking materials.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[dvd]

hey evelrod,

is that real mini's or the new things? I would be interested in any website info on your cars if available.

 

[MikeHalloran]

In my experience, powdercoat is _much_ more durable than any liquid paint, including polyurethane.

PEM studs installed with care but no Bondo will be hardly noticeable under the usual thick powdercoat... but they may be detectable on close examination.

If that's a concern, the 'blind' PEM studs, properly installed in a milled blind hole from the 'near side' are surprisingly tough.





Mike Halloran
Pembroke Pines, FL, USA

 

[MadMango]

Powder coating is going to give your thickest, toughest finish. Like other finish applications though, surface prep is important. Parts are washed, dried and cured on an automated line with repeatable results. At my last company we had our own powder coating line, so I was a bit spoiled.

About the only variable that is hard to control is the paint thickness, which can range between .010-.020" per side, much, much thicker in any closed corners. So this could be a design consideration. There are a bunch of different finishes you can have as well: high gloss, satin, flat, smooth, wrinkle, metallic flake, etc.

I agree that powder coating will hide a lot of blemishes and imperfections, and you will probably not need to use any body filler material. If it is a great concern, you might want to consider looking into welded studs (

http://www.studweldprod.com/),

in some applications they are better than PEM studs.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[bnrg]

Be aware that the powder coating cure (~400 F) for 30 or so minutes can have an effect on the strength of aluminum. I don't have access to my data but recollection is that 6061-t6 can lose 10% of strength due to the powder coat cure cycle. If you are using the aluminum in an as welded condition this might not be much of an issue as you have already reduced its strength, but it is something to keep in mind.

Bob

 

[sreid]

Is DuPont Imron still considered the "Gold Standard" for painted surfaces?

http://pc.dupont.com/Phantom/content/imron-comm.html

 

[evelrod]

Mike and MM:
The very thick coating in p coated subframes made for a very difficult assembly allignment to the existing chassis in my case. Had I to do it over, I would have used the same paint as I had used before. The chipping problem is a bit overstated as in either method, it was minimal. However the chips in the p coated parts were bigger/deeper.
Also, in certain applications, weight of finish is a possible concern as the p coated part is substantially heavier.

sreid:
I used Ditzler Dellthane on eairlier parts and finishes, but have use DuPont for the last ten years or so. Lots of new stuff to choose from, but the old paint systems still work just fine for me. Getting too old to learn all this new painting systems.

dvd:
Yes, it's a "real" Mini. Current race car is a '67 shell with as many of the original '63 Coopers parts as I could salvage. I run in the VARA CS class.
See

http://www.youtube.com

and type in "vintage Mini crash" then click on the Willow Springs crash...That was me in 2003. New car is much quicker.

For all:

A bit of nastalgia for the engineers on the forum that may find these videos "too" personal. Part 1 and part 2.

http://www.youtube.com/watch?v=CkTDCOQB-rg&feature=related

http://www.youtube.com/watch?v=W3jcIBPmYpY&feature=related

Rod

 

[PeterCharles]

Interesting video's, brought back memories.
Our college organised a trip for us engineering students to the Longbridge factory in the late 1960's.

 

[TVP]

sreid,

DuPont Imron is certainly one of the best coatings available for automobiles in terms of quality, aesthetics, etc. PPG and BASF also make top-of-the-line automotive coatings/paints.